LONDON, June 13 (Reuters) - Fast-fashion group Shein committed to engage on issues including sustainability and ethical labour policies when it was allowed to join the British Retail Consortium (BRC), the head of the industry body told Reuters.

Shein is stepping up preparations for a London listing but faces growing opposition from lawmakers, workers' rights campaigners and some retailers in the UK over alleged labour malpractices and its use of an import tax exemption.

The Chinese-founded company has said it is investing millions of pounds in strengthening governance and compliance across its supply chain and that its Modern Slavery Statement is available on its UK website, as required by law.

Shein's initial public offering (IPO) attempt in New York faced regulatory hurdles and pushback from lawmakers in the United States, where it is not a member of the National Retail Federation, which is the U.S. equivalent of the BRC.

Shein, which is also not a member of European trade body EuroCommerce, joined the BRC, which represents about 200 of Britain's biggest retailers, within the last year.

"The conversation with Shein joining is the same as it is with any member joining," said BRC CEO Helen Dickinson.

"Are they willing to engage in the subject areas that we think are important to the industry and if they are then they are welcome to come as members," she added.

Dickinson said the BRC's mission was to make a positive difference to the UK retail industry and its customers, with growth and investment, sustainability and ethical labour at the heart of its agenda.

"We don't see our job as being the regulator, the policeman, the due diligence decider," she said in an interview, adding that it was not up to the BRC to defend Shein or its policies.

"We don't defend any of our members, we defend our industry," she said.

"It is not our job to be responsible for the individual actions of any of our members, they are all grown up, responsible businesses."

Dickinson also said it would have been problematic to exclude Shein from the industry's main trade body as this could be viewed as anti-competitive.

Shein's mooted market capitalisation of more than 50 billion pounds ($64 billion) would be the equivalent of Tesco, Sainsbury's, Next, Marks & Spencer and JD Sports Fashion combined. ($1 = 0.7798 pounds) (Reporting by James Davey; Editing by Alexander Smith)